Joist hangers are used in building construction to secure the ends of joists or other members to headers or other support members. Typically, the joist hanger includes a u-shaped portion that receives the joist. The bottom surface of the joist rests on the seat of the hanger, and the side walls of the hanger are dimensioned to closely receive the side faces of the joist, providing it with lateral support.
Where appropriate, the joist may be connected to the hanger by means of nails driven through the side walls into the side faces of the joist. These nails may simply be driven horizontally into the joist, in which case they are preferably very short nails that will not pass through the joist. Alternatively, longer nails may be used that are driven horizontally and angularly into the joist such that they are driven into the header as well. This is often referred to as toe-nailing. The other common way to nail the hanger to the joist is to use short nails that are driven downward at an angle into only the joist.
Often, in order to connect the joist hanger to the header, back flanges are attached to the side walls. Generally, these flanges extend laterally from the side walls to overlap a portion of the face of the header. These flanges can extend inwardly or outwardly from the side walls, depending on design considerations.
Openings may be provided in the back flanges to receive fasteners. These fasteners are generally nails in light-frame wood construction. Screws and bolts are also used in wood construction, depending on the size of the members to be joined and other considerations. In light-gauge steel construction, sheet metal screws, bolts and rivets are commonly used.
In perhaps the simplest of hangers, the back flanges extend outwardly from the side flanges, providing an easily accessed fastening face. Fasteners are then driven through the back flanges into the header. In other instances, design considerations dictate which particular attachment method is used for attaching the joist and the hanger to the header.
In addition, top flanges may be attached to the back flanges to aid in the attachment to the header. If top flanges are used, the hanger is generally called a top-flange hanger. If no such top flanges are used, the hanger is generally called a face-mount hanger. If the top flanges wrap over the top of the header and down to the opposite face of the header the hanger is often called a wrap-around hanger. Again, various design considerations dictate what type of hanger and whether a top flange is used. Generally, if a top flange is used and the header is made of wood, pre-formed holes will be made in the top flange to receive suitable fasteners for connecting the top flange to the header.
As mentioned above, it is often desirable to connect the joist to the hanger. This is generally done to resist uplift forces on the joist. Such forces are often due to lateral loading on the building due to high winds or an earthquake. Also, one end of a joist must be downwardly restrained if that joist is cantilevered, for example, to support an overhanging deck. As mentioned above, to retain the joist within a conventional hanger, holes may be provided in the hanger side walls, through which nails are driven into the joist.
Using nails or screws to fix the joist to the hanger to resist uplift forces may be satisfactory when the joist is constructed from solid-sawn lumber or light gauge steel, but I-Joists are much more difficult to connect to a hanger with nails without splitting or damaging the chords of the I-Joist.
I-Joists have become more and more attractive as building materials as the cost of wood products has increased, because they generally use a third less lumber to provide similar performance as their solid-sawn counterparts, which generally makes them less expensive. Thus, the need has arisen to adequately address the problems of securing I-Joists against uplift.
Most sheet metal hangers designed to attach wood I-Joist members to a support member use one of three methods to resist uplift forces on the I-Joist. In the first method, two short joist nails are driven through the sides of the hanger into the bottom chord of the I-joist at a downward angle. It is especially important to put the nails in at a downward angle when using a laminated veneer I-Joist to prevent splitting of the bottom chord. In the second method, web stiffeners are attached to the web of the I-joist, and nails are driven into the web stiffeners. The joist can also be toe-nailed through the web stiffeners into the header for even greater uplift resistance. In the third method, prongs or tabs are bent inwardly from the side walls of the hanger seat and they either engage the top surface of the I-joist to hold it down or dig into the sides of the joist, if it lifts off the seat. Additional fasteners may or may not be used with methods that use tabs.
All of these methods have shortcomings. As mentioned above, any method that uses nails to connect the bottom chord to the hanger requires careful placement of the nails to prevent splitting of the bottom chord.
Furthermore, any method that uses nails must rely on the builder to go through the added step of actually installing the nails or using all the required nails, which can be time consuming and is sometimes ignored. Missing joist nails are difficult to detect through inspection because of their placement. Without joist nails, the bottom chord of the wood I-Joist is not properly secured for uplift capacity and can also be a source of floor squeaks.
Adding web stiffeners and then nailing or toe-nailing into the web stiffeners is time-consuming and material-intensive.
A number of different methods have been proposed for securing an I-Joist in a hanger against uplift forces that use tabs. A good overview of these methods is provided in U.S. Pat. No. 4,411,548, granted to J. Donald Tschan on Oct. 25, 1983 and also U.S. Pat. No. 5,564,248, granted to Gerald Callies on Oct. 15, 1996.
Most of the methods that rely on tabs or prongs to hold the joist down do not rely on the tabs alone, but use nails as well, raising all the problems that accompany nails. The first method that used a tab, and did not use nails, is taught by U.S. Pat. No. 4,411,548, and does not appear to have gained market acceptance. The second method is taught by U.S. Pat. No. 6,523,321 and is commercially available as Simpson Strong-Tie's IUS I-joist hanger.
The present invention, when used with an I-Joist, provides uplift resistance without using nails to secure the I-Joist to the hanger.
While a number of different methods have been proposed for resisting uplift of joists in light frame construction, up until now little has been done to address the generation of unnecessary noise due to the rubbing between the different parts of the connection as they loosen, which usually happens as the building settles and ages. This unnecessary and unwanted noise due to looseness of the parts is commonly referred to, and experienced, as “floor squeak.”
Among the prior art methods of securing a joist to a hanger, U.S. Pat. No. 5,564,248, granted to Gerald Callies, is probably the patent most concerned with addressing floor squeak. In his patent, Callies recognized that floor squeak can develop when the connection of the members making up the connection is loose. Callies '248 recognized that it is important to keep the bottom of the chord resting on the seat of the hanger to minimize floor squeak. To help keep the bottom of the I-Joist on the seat of the hanger, Callies '248 proposed that a downwardly, and inwardly projecting tab be formed in each side wall of the hanger that would bite into the side faces of the joist, and resist movement of the joist off of the seat of the hanger. It appears that Callies '248 did not mean for this tab to provide design load uplift resistance for the joist in most situations, but rather for nails to be used to provide design load uplift resistance, and for the tabs to prevent any uplift of the joist that might occur during the installation of the nails through the hanger and into the joist. Despite its concern with floor squeak, Callies '248 is silent about preventing floor squeak, except for statements about keeping the joist on the seat.
In addition to identifying noise problems associated with the joist lifting off of the seat of the hanger, the inventors have also found that it is important to keep the side walls spaced away from the hanger as much as possible, and to minimize any portions of the hanger that would lie between the top surface of the header and the sub-flooring.
The connection of the present invention improves on the prior art, and in particular that of Callies '248 and Tschan '548, by providing members which not only hold an I-Joist down onto the seat of the hanger without any additional operations having to be performed by the installer during the formation of the connection, but also push the joist away from the sides of the hanger while grabbing it firmly. Thus, in the present invention there is less contact between the joist and the hanger, so that less noise can be generated by the rubbing of the two parts should any looseness develop. Further, the two pieces are firmly held against each other, so that it is less likely for any looseness to develop.